Turbine Engine Comprising a Lobed Mixer Having Scoops

ABSTRACT

The invention relates to a lobed mixer ( 8 ) for arranging on the downstream end of a hood ( 4 ) separating the two co-axial streams, respectively inner and outer, the mixer ( 8 ) being shaped so as to have a least one peripheral succession of lobes ( 20, 21 ) which are generally radially oriented in relation to a longitudinal axis (LL′) of the mixer, each lobe ( 20, 21 ) forming a channel extending mainly along the longitudinal axis and comprising at least one peripheral succession of baffles ( 26 ) from the first stream to the second stream and/or from the second stream to the first stream, arranged on said lobes ( 20, 21 ).

TECHNICAL FIELD

The present invention relates to mixers of confluent gas streams in turbine engines, in particular bypass turbine engines.

PRIOR ART

Generally, a bypass turbine engine comprises an outlet exhaust nozzle in which the primary stream of the hot gases coming from the engine joins a secondary, cold air stream, propelled by a fan propeller.

Typically, an exhaust nozzle of this kind having confluent streams is composed of a primary cowl centred on the longitudinal axis of the turbine engine, a secondary cowl arranged concentrically with the primary cowl so as to define an annular channel for the flow of the secondary stream, and a central body defining, together with the primary cowl, a second annular channel for the flow of the primary stream, the secondary cowl extending beyond the primary cowl.

Generally, a mixer is mounted at the downstream end of the primary cowl, in particular in order to reduce the jet noise at the outlet of the exhaust nozzle by forcing the primary hot stream and the secondary cold stream to mix before they are discharged. Indeed, it is well known that acoustic gains are obtained by increasing the mixing between the cold stream and the hot stream leaving the turbine engine before they are discharged. From this point of view, it is useful for the streams to mix as quickly as possible, in the region of the path within the secondary cowl.

Among the exhaust nozzle mixers having confluent streams, the daisy-type mixer in the form of a sinusoidal portion defining inner lobes and outer lobes distributed over the entire circumference of the primary cowl of the exhaust nozzle is known in particular. In the case of a daisy-type mixer, the inner lobes form gutters that guide the cold stream radially towards the second channel in which the hot stream flows, and the outer lobes form gutters that guide the hot stream radially towards the channel in which the cold stream flows. Thus, at the outlet of the mixer, the cold stream and the hot stream mix together by shearing in a substantially radial direction.

This mixing makes it possible to generate vortexes of which the axis of rotation is overall axial and of which the intensity depends mainly on the conditions of discharge of the two streams and the conditions of supply of the base of the lobes of the mixer. However, these conditions do not always make it possible, in particular in the case of certain conditions of use of the turbine engine, such as the take-off phases of the aircraft, to achieve an efficiency of the mixer that is sufficient for reducing the intensity of the jet noise to the levels sought. Indeed, it is noted that the mixture of the streams may remain inhomogeneous over a distance equal to several times the outlet diameter of the exhaust nozzle before this inhomogeneity is absorbed.

Numerous optimisations of the shape of the lobes are used to improve the efficiency of a daisy-type lobed mixer by producing the least possible pressure drop. For example, the applicant proposed mixers having curved lobes in FR2902469 with the aim of producing a mix of the streams in the circumferential direction. In another design, as described in EP1870588, the radial inclination of the lobes induces an overall giratory movement of the streams that increases the effects of shearing between the streams.

The object of the present invention is to propose an alternative to the existing solutions with the aim of further improving the efficiency of a lobed mixer.

Description of the Invention

To this end, the invention relates to a lobed mixer intended to be placed at the downstream end of a cowl for separating the two coaxial ducts, namely the internal duct and the external duct, the mixer comprising at least one peripheral succession of lobes having a general radial orientation with respect to a longitudinal axis of the mixer, each lobe forming a gutter extending mainly along the longitudinal axis, and comprising at least one peripheral succession of scoops for passage from the first duct to the second duct and/or, inversely, from the second duct to the first duct, which scoops are placed on said lobes, at least one of said scoops being formed by an opening in a wall of the mixer in the region of the lobes, the opening being elongate in a given direction having a mainly axial component, and by a cover located entirely on either the first duct side or the second duct side with respect to said wall, said cover being connected to the edge of the opening apart from over a downstream portion, so as to form a hole for passage between the two ducts, the edge of said opening comprising two side portions which gradually diverge from one another going from upstream to downstream.

The scoop generates additional shearing upstream of the trailing edge of the mixer, which shearing is added to that generated by the lobes.

This type of scoop corresponds to flush scoops, which suck in the flow on one side and expel it on the other. The specific shape of the scoops used causes a slight pressure drop in the flow as it passes through said scoops.

In addition, designing the opening so as to be flared or so as to spread gradually from upstream to downstream makes it possible for a portion of the flow at the outlet of the scoop to flare out and form vortex structures that amplify and homogenise the effects of mixing between the cold stream and the hot stream, and this further limits the levels of jet noise reduction obtained during the take-off phases of the aircraft.

The two side portions at the edge of the opening may give said opening a convex shape.

According to another feature of the invention, the cover has a flat portion which corresponds to the shape of the opening and which gradually diverges from the wall of the lobe so as to form a slope.

A plurality of said scoops may be arranged between the base lines of the gutters formed by two successive lobes in the circumferential direction. In other words, at least one side wall of a lobe may comprise a plurality of said scoops. A design of this kind makes it possible to increase the effect of tangential shearing of the flush scoops.

In a particular embodiment, the mixer comprises scoops of which the cover is located on the second duct side.

Said lobed mixer may also comprise scoops of which the cover is located on the first duct side.

Two scoops having different elongation directions may be arranged between base lines of the gutters formed by two successive lobes in the circumferential direction. In other words, at least one side wall of a lobe may comprise two scoops having different elongation directions.

At least one scoop for passage between the first duct to the second duct and one scoop for passage from the second duct to the first duct may be arranged between base lines of the gutters formed by two successive lobes in the circumferential direction.

In said lobed mixer, said lobes may form gutters of which the base lines, having alternately a positive angle of incidence and a negative angle of incidence in the downstream direction with respect to the longitudinal axis, are circumferentially successive.

The invention also relates to a turbine engine comprising a lobed mixer as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood and other details, features and advantages of the present invention will become clearer upon reading the following description with reference to the accompanying drawings, in which:

FIG. 1 is a schematic axial section of a turbine engine using the invention.

FIG. 2 is a rear, perspective view of a first variant of the lobed mixer according to the invention.

FIG. 3a is a schematic perspective view of a scoop used for the invention, as seen from the front from the side where the flow is sucked in.

FIG. 3b is a schematic perspective view of a scoop used for the invention, as seen from the front from the side where the flow that has been sucked in emerges.

FIG. 4a is a perspective view of a lobe of the mixer according to a first embodiment of the invention.

FIG. 4b shows the lobe from FIG. 4a , as seen from the rear of the mixer.

FIGS. 5a, 5b and 5c show different variants of the first embodiment of a lobe of the mixer, as seen in a perspective view.

FIG. 6a is a perspective view of a lobe of the mixer according to a second embodiment of the invention.

FIG. 6b shows the lobe from FIG. 6a , as seen from the rear of the mixer.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

The invention relates, for example, to a bypass turbine engine such as that shown schematically in FIG. 1. The type of turbine engine in which it is intended for the invention to be used is generally rotationally symmetrical about the longitudinal axis LL′ thereof. As per convention, the concepts of radius, axial plane and transverse plane are used in the description with respect to said axis LL′. Otherwise, the concepts upstream and downstream are in this case taken to be along the axis LL′ with reference to the main direction of the flows in the turbine engine, as shown by the arrows F₀, F₁ and F₂.

Here the turbine engine comprise a nacelle 1 which surrounds the turbine engine and which an air stream F₀ enters. This air stream F₀ is driven by a fan 2, at the outlet of which said air stream is split into an air stream that passes into the engine 3 and a secondary air stream F₂ that passes between the nacelle 1 and a cowl 4 surrounding the engine 3. The gases leaving the engine 3 form a primary gas stream F₁, which meets the secondary air stream F₂ at the downstream end of the cowl 4 of the engine 3.

In the example shown, although not limiting, the cowl 4 and a central body 5 form a primary duct 6 of the primary stream F₁, having an annular shape, while the cowl 4 and the nacelle 1 form a secondary duct 7 of the secondary stream F₂, which secondary duct is also annular. Similarly, here the ducts 6, 7 converge in a duct surrounded by the nacelle 1, although they may converge outside the nacelle 1 in other turbine engine designs.

The invention relates more particularly to a lobed mixer 8, which here is placed at the convergence of the primary duct 6 and the secondary duct 7.

With reference to FIG. 2, the lobed mixer 8 according to the invention comprises a substantially cylindrical portion 8 a, which is connected to the downstream end of the cowl 4, and an undulating end 8 b, downstream of a transverse section 9, that is intended to divert the primary stream F₁ and the secondary stream F₂ in order to encourage them to mix. Said undulating end 8 b has a downstream edge 18 forming the downstream end of the mixer 8.

In the following description, the terms “inner”, “inside” or “inwards” and “outer”, “outside” or “outwards” denote an element of the mixer, or the surroundings thereof, as being close to and remote from the longitudinal axis LL′, respectively.

The undulating end 8 b comprises a series of substantially sinusoidal undulations that define a series of inner lobes 20 and outer lobes 21, of the daisy type. The inner lobes 20 and the outer lobes 21 of the mixer are arranged so as to alternate and may be evenly distributed over the entire circumference of the mixer 8.

As shown in FIG. 2, an inner lobe 20 can be defined as a gutter comprising side walls 22, 23 that are interconnected along a base line 24, which defines the minimum radius of the lobe 20 in a transverse section. Said base line 24 extends radially inwards starting from the transverse section 9 in the axial direction LL′. The two side walls diverge from the base line 24, going outwards, and this defines a general radial orientation of said lobe, which orientation is directed inwards.

Inversely, an outer lobe 21 can also be defined as a gutter comprising side walls 23, 22 having a common longitudinal edge that corresponds, this time, to a base line 25 extending radially outwards starting from the transverse section 9 in the axial direction LL′. Said two side walls diverge from the base line 25, going outwards, which base line in this case defines the maximum radius of the outer lobe 21, and this defines a general radial orientation of said lobe, which orientation is directed outwards.

Here, a lobe, whether inner 20 or outer 21, can be considered to share its side walls with the adjacent lobes, a side wall 22, 23 having, as opposite longitudinal edges, two successive backbone lines 24, 25 that extend radially in opposite directions.

Advantageously, the side walls 22, 23 are continuously interconnected tangentially on the base lines 24, 25. Said walls therefore have a rounded transverse profile in this region. Also advantageously, said walls have an substantially flat intermediate portion between the rounded ends thereof.

Said flat intermediate portion may be substantially oriented along a radial plane of the turbine engine. The inner lobes 20 and the outer lobes 21 may not have the same circumferential width. Generally, the outer lobes 21 are narrower than the inner lobes 20.

The base lines 24 of the inner lobes 20 may extend further downstream than the base lines 25 of the inner lobes 21. Moreover, the side walls 22, 23 end downstream at a downstream edge belonging to the downstream end 18 of the mixer 8.

Moreover, the inner lobs 20 project radially inside the casing 4, i.e. they pass into the extension of the primary duct 6, while the outer lobes 21 project radially outside the casing 4, i.e. they pass into the extension of the secondary duct 7.

With reference to FIG. 2, an outer lobe 21 therefore forms a gutter that mainly guides the primary flow F₁ outwards, and an inner lobe 20 forms a gutter that mainly guides the secondary flow F₂ inwards, at the outlet of the mixer 8. In this way, overall radial shearing is generated between the primary stream F₁ and the secondary stream F₂ at the outlet of the lobed mixer 8, thus encouraging said streams to mix.

In a preferred embodiment of the invention, with reference to FIGS. 2 and 4, a scoop 26 is installed on each side face 22, 23 of the lobes, so as to draw a portion F′₁ of the primary flow flowing along the side wall 22, 23 in the outer lobe 21 in order to blow it into the inner lobe 20. Preferably, this scoop 26 is installed in the substantially flat portion of the side wall 22, 23.

Preferably, with reference to FIGS. 3a and 3b , said scoop is a flush scoop.

A flush scoop 26 comprises an opening made in the side wall 22, 23, which is elongate in a given direction Y. Here the direction Y is oriented in a direction such that it forms a slight angle, even zero, with the current lines C of the primary flow F₁ stream flowing along the side wall. The direction Y can therefore be considered to be oriented from upstream to downstream.

The opening widens from upstream to downstream, between side edges 30, 31, and comprises a downstream edge 33 substantially transverse to the direction Y.

The scoop 26 also comprises a cover 34, which in this case is located entirely on the inner lobe 20 side with respect to the side wall, said cover 34 being connected to the edges 30, 31 of the opening apart from over the downstream edge 33, so as to form a hole for communication between the two sides of the side wall 22 of the lobe. Here, for example, the cover 34 has substantially a flat portion which corresponds to the shape of the opening and which is connected to the side edges of the opening by substantially transverse walls. Moreover, the flat portion gradually diverges from the side wall 22 of the lobe, so as to form a slope that leads onto the outlet hole of the scoop 26.

Here, the side edges 30, 31 of the opening have an angle of divergence that increases going downstream, thus giving a convex shape to the opening. This can produce the effect of a diverging nozzle which sucks in the flow F′₁ that follows the slope formed by the cover 34.

In this way, as is shown in FIGS. 3a and 3b , the portion F′₁ of the primary-stream flow is sucked in along the cover so as to lead into the secondary stream F₂ via the outlet hole, at a general orientation given by the orientation Y of the opening, following the inclination of the slope of the cover 34. This flow F′₁ also flares out following the angle of divergence between the side edges 30, 31 of the opening as it leaves the scoop 26.

The scoop 26 therefore produces, in the region thereof, a tangential shearing effect in addition to that produced at the downstream end 18 of the lobes 20, 21. Furthermore, as is indicated by FIGS. 3a and 3b , the portion F′₁ of the primary flow passing through said scoop tends, as it passes through, to form vortex structures that amplify the effects of mixing with the secondary stream, portion F₂, that said primary stream meets at the outlet of the scoop 26.

This first embodiment, with reference to FIGS. 4a and 4b , has a scoop 26 which is located substantially at the centre of each side wall 22, 23, in line with the axial and radial directions, and of which the orientation direction Y is substantially aligned with the current lines of the primary stream F₁ and of the secondary stream F₂.

In the variants shown in FIGS. 5a, 5b and 5c , the position and the orientation of the scoop 26 may be modified. In FIGS. 5a and 5b , the orientation Y of the scoop 26 may form a positive or negative angle of incidence (converging and diverging) with respect to the longitudinal axis LL′, so as to produce an incidence effect. In FIG. 5c , the axial position of the scoop 26 is moved so as to alter the interaction of the shearing generated thereby with that generated by the lobes 20, 21, at the outlet 18 of the mixer 8.

In a second embodiment, with reference to FIGS. 6a and 6b , a first scoop 26 as described above is associated, on the same side wall, with a second scoop 27, which is similar to the first scoop but is inverted with respect to the crossing-over of the side wall 22, 23 between the inner lobe 20 and the outer lobe 21. The second scoop 27 therefore has the effect of sending a portion F′₂ of the secondary stream into the primary stream F₁, thus passing into the outer lobe 21. Said scoop therefore produces, this time, an effect of additional mixing in the outer lobe 21.

The design shown in FIGS. 6a and 6b places the second scoop 27 upstream of the first scoop 26. It is, however, conceivable for the reverse to be implemented. In addition, the different variants, shown in FIG. 5a-5c , of the position and the orientation of the scoop 26 of the first embodiment can of course be applied to each of the two scoops 26, 27 of this embodiment. Thus, the designs shown in FIGS. 5c and 6a-6b may be generalised, and it is then possible, according to the invention, to arrange a plurality of scoops on at least one lobe, it being possible to adapt the size of the scoops in order to arrange a number of scoops greater than two. 

1. A lobed mixer, intended to be placed at the downstream end of a cowl for separating the two coaxial ducts, namely the internal duct and the external duct, the mixer comprising at least one peripheral succession of lobes having a general radial orientation with respect to a longitudinal axis of the mixer, each lobe forming a gutter extending mainly along the longitudinal axis, and comprising at least one peripheral succession of scoops for passage from the first duct to the second duct and/or, inversely, for passage from the second duct to the first duct, which scoops are placed on said lobes, at least one of said scoops being formed by an opening in a wall of the mixer in the region of the lobes, the opening being elongate in a given direction having a mainly axial component, and by a cover located entirely on either the first duct side or the second duct side with respect to said wall, said cover being connected to the edge of the opening apart from over a downstream portion, so as to form a hole for passage between the two ducts, characterised in that the edge of said opening comprises two side portions which gradually diverge from one another going from upstream to downstream.
 2. The lobed mixer according to claim 1, wherein the two side portions at the edge of the opening give said opening a convex shape.
 3. The lobed mixer according to claim 1, wherein the cover has a flat portion which corresponds to the shape of the opening and which gradually diverges from the wall of the lobe so as to form a slope.
 4. The lobed mixer according to claim 1, wherein the lobed mixer comprising a plurality of said scoops between the base lines of the gutters formed by two successive lobes in the circumferential direction.
 5. The lobed mixer according to claim 1, wherein the lobed mixer comprising two scoops having different elongation directions between the base lines of the gutters formed by two successive lobes in the circumferential direction.
 6. The lobed mixer according to claim 1, wherein the lobed mixer comprising at least one scoop for passage from the first duct to the second duct and one scoop for passage from the second duct to the first duct, between the base lines of the gutters formed by two successive lobes in the circumferential direction.
 7. The lobed mixer according to claim 1, wherein said lobes form gutters of which the base lines, having alternately a positive angle of incidence and a negative angle of incidence in the downstream direction with respect to the longitudinal axis are circumferentially successive.
 8. A turbine engine comprising a lobed mixer according to claim
 1. 